Control systems have input signals (input points or input objects), output signals (output points or output objects), internal values (internal points), and logic. Typically, the inputs are read, logic is performed, internal values (which may be intermediate resultsxe2x80x94results that are not of value themselves, but are used in subsequent logicxe2x80x94or final resultsxe2x80x94results that are the end produce of the logic) are updated, and outputs are generated.
For safe operation and maintenance of the control systems, the user must at times determine what effect or interactions there would be from changes to a point or object (i.e., determine what can be influenced by changes to some parameter of a particular point). Similarly, the user must at times determine what could be influencing a parameter of a particular point. An example of xe2x80x9ca parameter of a particular pointxe2x80x9d would be the current value in gallons per minute of the inlet flow to tank number 1.
When a measurement instrument is to be serviced, its signal will change (often dramatically). This change may cause the control system to take unexpected actions based upon either straightforward or convoluted linkages within the control logic. The potential effect must be determined prior to working on the instrument, so that preparations can be made to avoid any problems with the process. If the value of an internal or output point is not as expected, the cause must be determined in order to evaluate whether this is an error or correct.
Determining how these various points or objects (input, output and internal) are related is traditionally done by hand, with the use of simple cross-references and listings of the logic. An example would be the cross-references provided by the documentation packages provided with most PLC""s (programmable logic controllers) and their ladder logic listings.
When looking for what can influence a particular point, the engineer first looks it up in the cross-reference to see where the point is used. Then, looking at that particular referenced portion of logic, he determines what other points could affect this point. Next, these points must in turn be looked up to see what could affect them, and so on until all points that could affect this point are found.
Similarly, to determine what a particular point can influence, the engineer first looks it up in the cross-reference to see where the point is used. Then, looking at that particular referenced portion of logic, he determines what other points could be affected by this point. Next, these points must in turn be looked up to see what they could affect, and so on until all points that could be affected are found. This is a time consuming and tedious method. Further, it is easy to make a mistake and miss an affected point. The present invention provides a rapid, accurate method to visualize and represent these process insertions.
The present invention is a method and apparatus for identifying and displaying process interactions. Process data points are identified and inputted into a computer along with a logic network relating to these points. A computer program operates through the logic network to analyze the interactions of the points. A tabulation of the interactions found is created in the program and stored as a database. Upon query regarding a particular data point, the tabulation is presented in a readable format on a screen of said computer.